Solid electrolytic capacitor and method for producing the same

ABSTRACT

A solid electrolytic capacitor comprising a capacitor element obtainable by compressing a porous valve-acting metal substrate having on the dielectric film surface thereof a solid electrolyte layer containing an electrically conducting polymer in the thickness direction, wherein assuming that the maximum thickness and the minimum thickness of the electrically conducting polymer layer including the substrate before the compression are Hamax and Hamin, and the maximum thickness and the minimum thickness of the electrically conducting polymer layer after the compression are Hbmax and Hbmin, the percentage decrease ΔH in the difference of thickness represented by the following formula is preferably from 5 to 95%: Formula (I). The thin solid electrolytic capacitor element of the present invention, which can be stably produced with a small variety in shape, enables fabrication of a solid electrolytic multilayer capacitor having a high-capacitance and small-size with a low height, which, free from short-circuit failure, exhibits stable performance 
     
       
         
           
             
               
                 
                   
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CROSS-REFERENCE TO RELATED APPLICATION

This is an application based on the prescription of 35 U.S.C. Section111(a) with claiming the benefit of filing date of U.S. Provisionalapplication Ser. No. 60/430,063 filed Dec. 2, 2002 under the provisionof 35 U.S.C. Section 111(b), pursuant to 35 U.S.C. Section 119(e)(1).

TECHNICAL FIELD

The present invention relates to a solid electrolytic capacitor using anelectrically conducting polymer as a solid electrolyte layer, and aproduction method thereof.

BACKGROUND ART

A basic element of a solid electrolytic capacitor is generally produced,as shown in FIG. 1, by forming an oxide film layer 2 as a dielectricmaterial on an anode substrate 1 comprising a metal foil having aspecific surface area enlarged through etching treatment, forming asolid semiconductor layer (hereinafter referred to as a solidelectrolyte) 4 as an opposing electrode in the outer side of the oxidefilm layer, and if desired, further forming an electrically conductinglayer 5 such as electrically conducting paste. To an element thusobtained or elements stacked, lead wires 6 and 7 are joined and theentire is completely molded with an epoxy resin 8 or the like. Thethus-produced element is being widely used as a capacitor 9 componentfor electrical products.

With recent progress on digitization of electric equipment andspeeding-up of PC operation, a small-size large-capacitance capacitorand a capacitor having a low impedance in the high frequency region aredemanded. Recently, use of an electrically conducting polymer havingelectron conductivity as a solid electrolyte has been proposed.

As for the shape of solid electrolyte, a technique in which, by weldinga metal to an aluminum foil, an electrolytically polymerized conductivepolymer is formed all over the surface of an aluminum foil with themetal being as the starting part of polymer growth through electrolyticoxidation has been proposed (see, for example, JP-A-4-307917, (the term“JP-A” as used herein means an “unexamined published Japanese patentapplication”)).

Also, for the purpose of enhancing electrostatic capacitance or reducingthe size, aggressive development on technique of enlarging the effectivesurface area of the anode foil is being made. For example, a techniqueof etching an aluminum foil and then rolling the etched layer has beenproposed (see, for example, Japanese Patent Number 3084330 andJP-A-14-260968).

Furthermore, a small-size and high-density semiconductor package isdemanded, and a thin and substrate-contacting solid electrolyticcapacitor which is incorporated into a substrate has been proposed (see,for example, JP-A-14-260967).

DISCLOSURE OF INVENTION

In order to obtain a capacitor having a predetermined capacitance, asolid electrolytic capacitor is usually produced by stacking a pluralityof capacitor elements, connecting an anode lead wire to the anodeterminal, connecting a cathode lead wire to the electrically conductinglayer containing an electrically conducting polymer, and sealing theentire with an insulative resin such as an epoxy resin. However, in asolid electrolytic capacitor, if the polymerization conditions are notprecisely controlled in the step of attaching an electrically conductingpolymer to the cathode part, the thickness of the electricallyconducting polymer attached becomes uneven, and the electricallyconducting polymer is too thin in some portions, giving rise to problemssuch that the paste or the like readily comes into direct contact withthe oxide dielectric film layer to cause increase in the leakagecurrent. Therefore, it is necessary for the electrically conductingpolymer to have a sufficient thickness. Since the number of capacitorelements which can be stacked in a predetermined chip is restricted bythe thickness of the element, desirable capacitance of solidelectrolytic capacitor has not been achieved. Moreover, if the thicknessof the electrically conducting polymer attached is uneven, thecontacting area between the stacked capacitor elements becomes small,giving rise to a problem that the equivalent series resistance (ESR)becomes large.

Precise control of polymerization conditions for a long time of period,which is required for obtaining an electrically conducting polymer witha smaller variety in thickness, raises a problem that such a requirementgreatly deteriorates the productivity.

Therefore, with a view to solving the above-described problems, theobjects of the present invention are, to fabricate a solid electrolyticmultilayer capacitor having a high capacitance and a low equivalentseries resistance by stably producing thin elements having a smallervariety in shape to increase the number of elements to be stacked insidethe capacitor with the time involved for precisely controlling polymerformation being reduced without increasing in short-circuit failurerate, and to provide a production process therefor.

As a result of extensive investigations to attain these objects, thepresent inventors have found that the shape of the solid electrolyte canbe effectively made even by compressing the electrically conductingpolymer formed and the thus-obtained solid electrolytic capacitor isenhanced in adhesive property of the solid electrolyte formed on thedielectric film, favored with high capacitance, reduced in thedielectric loss (tan δ), leakage current and defective rate.

It has been also found that by stacking a plurality of theabove-described solid electrolytic capacitor elements having excellentproperties, a capacitor reduced in the size and elevated in thecapacitance can be produced.

That is, the present invention provides the following solid electrolyticcapacitors and production method therefor.

-   1. A solid electrolytic capacitor comprising a capacitor element    obtainable by compressing a porous valve-acting metal substrate    having on the dielectric film surface thereof a solid electrolyte    layer containing an electrically conducting polymer in the thickness    direction.-   2. The solid electrolytic capacitor as described in 1 above, wherein    in the capacitor element, the porous valve-acting metal substrate    having on the dielectric film surface thereof a solid electrolyte    layer containing an electrically conducting polymer is compressed in    the thickness direction and a cathode layer is provided on the solid    electrolyte layer.-   3. The solid electrolytic capacitor as described in 1 or 2 above,    wherein the solid electrolyte containing an electrically conducting    polymer to be provided on the dielectric film on the porous    valve-acting metal is formed by chemical polymerization or    electrochemical polymerization.-   4. The solid electrolytic capacitor as described in any one of 1 to    3 above, wherein the thickness of the element having thereon a solid    electrolyte layer has a maximum height (Rmax) of 250 μm or less    after the compression.-   5. The solid electrolytic capacitor as described in 2 above,    comprising a capacitor element obtained by compressing a porous    valve-acting metal substrate having on the dielectric film surface    thereof a solid electrolyte layer containing an electrically    conducting polymer in the thickness direction to homogenize the    thickness of the electrically conducting polymer layer and then    providing a cathode layer on the solid electrolyte layer.-   6. The solid electrolytic capacitor as described in any one of 1 to    5 above, wherein, assuming that the maximum thickness and the    minimum thickness of the electrically conducting polymer layer    including the substrate before the compression are Hamax and Hamin,    respectively, and that the maximum thickness and the minimum    thickness of the electrically conducting polymer layer including the    substrate after the compression are Hbmax and Hbmin, respectively,    the percentage decrease ΔH in the difference of thickness    represented by the following formula is within a range of 5 to 95%:

${\Delta\;{H(\%)}} = {\left\lbrack {1 - \frac{\left( {{{Hb}\;\max} - {{Hb}\;\min}} \right)}{\left( {{{Ha}\;\max} - {{Ha}\;\min}} \right)}} \right\rbrack \times 100.}$

-   7. The solid electrolytic capacitor as described in any one of 1 to    6 above, wherein the compressibility of the entire substrate having    thereon a solid electrolyte layer is from 5 to 90%.-   8. The solid electrolytic capacitor as described in any one of 1 to    7 above, wherein the electrically conducting polymer as the solid    electrolyte is formed on the valve-acting metal substrate having a    dielectric film by solution chemical oxidative polymerization or    vapor-phase chemical oxidative polymerization using a monomer of an    organic polymer.-   9. The solid electrolytic capacitor as described in any one of 1 to    7 above, wherein the electrically conducting polymer as the solid    electrolyte is formed by repeating an operation of alternately    dipping the valve-acting metal substrate having a dielectric film in    a solution containing a monomer of an organic polymer and in a    solution containing an oxidizing agent.-   10. The solid electrolytic capacitor as described in any one of 1 to    9 above, wherein the porous valve-acting metal substrate has a    plate- or foil-like shape.-   11. The solid electrolytic capacitor as described in any one of 1 to    10 above, wherein the porous valve-acting metal is a simple metal    selected from a group consisting of aluminum, tantalum, niobium,    titanium, zirconium, magnesium and silicon, or an alloy thereof.-   12. The solid electrolytic capacitor as described in any one of 1 to    11 above, wherein the monomer of the organic polymer for forming the    electrically conducting polymer is a compound containing a 5-member    heterocyclic ring, or a compound having an aniline skeleton.-   13. The solid electrolytic capacitor as described in 12 above,    wherein the compound containing a 5-member heterocyclic ring is a    compound having a thiophene skeleton or a polycyclic sulfide    skeleton.-   14. The solid electrolytic capacitor as described in 13 above,    wherein the monomer compound having a thiophene skeleton is    3-ethylthiophene, 3-hexylthiophene, 3,4-dimethylthiophene,    3,4-methylenedioxythiophene or 3,4-ethylenedioxythiophene.-   15. The solid electrolytic capacitor as described in any one of 1 to    14 above, wherein a part of the solid electrolyte layer formed of    the electrically conducting polymer has a lamella structure or a    fibril structure.-   16. A solid electrolytic multilayer capacitor obtained by stacking a    plurality of capacitor elements described in any one of 1 to 15    above.-   17. A solid electrolytic multilayer capacitor comprising a capacitor    element obtained by stacking a plurality of porous valve-acting    metal substrates each having on the dielectric film surface thereof    a solid electrolyte layer comprising an electrically conducting    polymer resulting from oxidative polymerization of a monomer of an    organic polymer with an oxidizing agent, compressing the multilayer    substrate in the thickness direction, and providing a cathode layer    on the outer surface of the solid electrolyte layer.-   18. The solid electrolytic multilayer capacitor as described in 17    above, wherein the compressibility of the entire multilayer    substrate having provided thereon solid electrolyte layers is from 5    to 90%.-   19. A method for producing a solid electrolytic capacitor,    comprising forming a solid electrolyte layer of an electrically    conducting polymer on the surface of a porous valve-acting metal    substrate having a dielectric film by using a solution containing a    monomer for forming an electrically conducting polymer under the    action of an oxidizing agent and a solution containing an oxidizing    agent, compressing the substrate having provided thereon an    electrically conducting polymer in the thickness direction and    providing a cathode layer on the solid electrolyte layer.-   20. A method for producing a solid electrolytic capacitor,    comprising forming a solid electrolyte layer of an electrically    conducting polymer on the surface of a porous valve-acting metal    substrate having a dielectric film by using a solution containing a    monomer for forming an electrically conducting polymer under the    action of an oxidizing agent and a solution containing an oxidizing    agent, stacking a plurality of substrates each having provided    thereon an electrically conducting polymer, compressing the    multilayer substrate in the thickness direction and providing a    cathode layer on the outer surface of the solid electrolyte layer.-   21. A method for producing a solid electrolytic capacitor,    comprising forming a solid electrolyte layer of an electrically    conducting polymer on the surface of a porous valve-acting metal    substrate having a dielectric film by using a solution containing a    monomer for forming an electrically conducting polymer under the    action of an oxidizing agent and a solution containing an oxidizing    agent, compressing the substrate having provided thereon an    electrically conducting polymer in the thickness direction,    providing a cathode layer on the solid electrolyte layer, and    compressing the cathode layer in the thickness direction.-   22. The method for producing a solid electrolytic capacitor as    described in any one of 19 to 21, wherein the entire substrate    having provided thereon a solid electrolyte layer is compressed at a    compressibility of 5 to 90%.-   23. The method for producing a solid electrolytic capacitor as    described in any one of 19 to 21, wherein assuming that the maximum    thickness and the minimum thickness of the electrically conducting    polymer layer including the substrate before the compression are    Hamax and Hamin, respectively, and that the maximum thickness and    the minimum thickness of the electrically conducting polymer layer    including the substrate after the compression are Hbmax and Hbmin,    respectively, the compression is performed such that the percentage    decrease ΔH in the difference of thickness represented by the    following formula is within a range of 5 to 95%:

${\Delta\;{H(\%)}} = {\left\lbrack {1 - \frac{\left( {{{Hb}\;\max} - {{Hb}\;\min}} \right)}{\left( {{{Ha}\;\max} - {{Ha}\;\min}} \right)}} \right\rbrack \times 100.}$

-   24. The method for producing a solid electrolytic capacitor as    described in any one of 19 to 23 above, which comprises a    re-electrochemical formation step after the step of compressing the    substrate having provided thereon a solid electrolyte layer in the    thickness direction.-   25. The method for producing a solid electrolytic capacitor as    described in any one of 19 to 23 above, which comprises a    humidification aging step after the step of compressing the    substrate having provided thereon a solid electrolyte layer in the    thickness direction.-   26. The method for producing a solid electrolytic capacitor as    described in 25 above, wherein the humidification aging step is    performed at an electrochemical forming voltage lower than the    sparking voltage under the conditions of 20 to 95° C. and 40 to 95%    RH.

The method of the present invention is described below by referring tothe drawings attached.

The dielectric film 2 on the surface of the substrate 1 for use in thepresent invention is usually formed, for example, by electrochemicallyforming a porous shaped article of a valve-acting metal.

The electrochemical forming conditions such as electrochemical formingsolution and electrochemical forming voltage for use in theelectrochemical formation are adjusted to appropriate conditions whichhave been confirmed through experiments performed in advance, accordingto the capacitance, breakdown voltage and the like required for thesolid electrolytic capacitor to be produced. In the electrochemicalformation, the masking 3 is generally provided so as to prevent theelectrochemical forming solution from soaking up to the portion which ispredetermined to be the anode of the solid electrolytic capacitor and atthe same time, the masking ensures the insulation from the solidelectrolyte 4 (cathode portion) which is formed in a later step.

The masking material is not limited but, for example, a generalheat-resistant resin, preferably a solvent-soluble or solvent-swellableheat-resistant resin, a precursor thereof or a composition comprising aninorganic fine powder and a cellulose-base resin, may be used. Specificexamples thereof include polyphenylsulfone (PPS), polyethersulfone(PES), cyanic ester resin, fluororesin (e.g., tetrafluoroethylene,tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), low molecularpolyimide, and derivatives and precursors thereof. Among these, lowmolecular polyimide, polyether sulfone, fluororesin, and precursorsthereof are preferred.

In general, examples of methods for forming an electrically conductingpolymer on an oxide dielectric film include a method of forming anelectrically conducting polymer layer by vapor phase polymerization orelectrolytic polymerization (see, JP-A-3-6217), a solution chemicalpolymerization method of adhering a monomer of an organic polymer on theoxide dielectric film and polymerizing the monomer in an oxidizing agentsolution (see, JP-A-11-251191), and an electrochemical polymerizationmethod where the point of feeding electricity to the anode body isshifted at predetermined time intervals by using a switching device tothereby obtain a uniform thickness of the electrically conductingpolymer layer (see, U.S. Pat. Nos. 6,168,639 and 6,313,979). In thepresent invention, solution chemical oxidative polymerization of amonomer of an organic polymer, containing steps of dipping a porousvalve-acting metal substrate in an oxidizing agent solution and dryingit to gradually increase the concentration of the oxidizing agentsolution on the substrate, or vapor phase chemical oxidativepolymerization is preferably used. In particular, solution chemicaloxidative polymerization is more preferred.

According to the present invention, as shown in Examples laterdescribed, an aluminum foil having an oxide dielectric film is dipped,for example, in an isopropyl alcohol (IPA) solution of3,4-ethylenedioxythiophene (EDT), air-dried to mostly remove the IPA,and dipped in an aqueous solution, containing about 20 mass % of anoxidizing agent (ammonium persulfate). Then, by heating at about 40° C.for 10 minutes or by repeating the process, the polymer ofpoly(3,4-ethylenedioxythiophene) can be obtained.

The solid electrolyte layer of an electrically conducting polymer formedby the method of the present invention has a fibril structure or alamella (thin layer-like) structure. Widespread overlapping among thepolymer chains in these structures, which facilitates hopping ofelectrons, is considered to contribute to improvement in the electricconductivity and in properties such as low impedance.

In the solution chemical polymerization method, a monomer is attachedonto a dielectric film having microfine pores on an anode substrate,oxidative polymerization thereof is induced under the action of anoxidizing agent and moisture in air in the presence of a compound whichcan work out to a dopant of the electrically conducting polymer, and thepolymer composition produced on the dielectric surface forms a solidelectrolyte. At this time, for forming a good polymer composition, thedipping time (impregnation time) in each of the monomer-containingsolution and the oxidizing agent-containing solution must be adjusted tocontrol the amount of the monomer attached and the amount of theoxidizing agent attached. For example, if the dipping time is too long,the polymerization reaction cannot be completed and the polymercomposition obtained is liable to have a low molecular weight. Also, ifthe dipping time in the oxidizing agent-containing solution having anunsaturated concentration is too long, the oxidizing agent which hasbeen attached to the metal foil substrate through previous stepsincluding the drying step re-dissolves and at the same time, the monomerattached or the polymer produced is also eluted or flows out, as aresult, not only the production of the polymer is retarded but also theoxidizing agent-containing solution is contaminated with the effluent.The same may occur in the case of dipping in the monomer-containingsolution.

With respect to the phenomenon which may be brought about, there mayoccur, for example, coloration of the oxidizing agent-containingsolution or monomer-containing solution due to low molecular weightcomponents, suspension of the polymerized material, tendency toward thereduction in the weight of the adhered and formed solid electrolyte, andchange in the viscosity or specific gravity of the monomer-containingsolution.

Accordingly, in the method of the present invention, the dipping time ineach of the monomer-containing solution and the oxidizingagent-containing solution is from a time sufficiently long to allow themonomer component or oxidizing agent component in the solutioncontaining the component to adhere to the dielectric surface of themetal foil substrate to a time period less than 15 minutes, preferablyfrom 0.1 second to 10 minutes, more preferably from 1 second to 7minutes.

After the impregnation in the monomer-containing solution, the substratemust be left standing in air for a predetermined time to vaporize thesolvent and thereby uniformly attach the monomer to the dielectricsurface and to the polymer composition. The conditions therefor varydepending on the kind of solvent but generally, the standing temperatureis from 0° C. to the boiling point of the solvent and the standing timeis from 5 seconds to 15 minutes. For example, in the case of analcohol-type solvent, standing for 5 minutes or less may be sufficient.With this standing time, the monomer can uniformly adhere to thedielectric surface and at the subsequent dipping in the oxidizingagent-containing solution, the contamination can be reduced.

After the dipping in the monomer-containing solution and in theoxidizing agent-containing solution, the substrate is held in an air ata constant temperature for a predetermined time to allow the oxidativepolymerization of the monomer to proceed.

The polymerization temperature varies depending on the kind of themonomer, however, for example, in the case of pyrrole, thepolymerization temperature is 5° C. or less and in the case of athiophene-type monomer, from about 30 to 60° C.

The polymerization time depends on the amount of the monomer to beattached at the dipping. The amount of the monomer attached variesdepending on the concentration, viscosity or the like of themonomer-containing solution and the oxidizing agent-containing solutionand cannot be indiscriminately specified, however, in general, when theamount of the monomer attached per once is small, the polymerizationtime can be short, whereas when the amount of the monomer attached peronce is large, the polymerization takes a long time.

In the method of the present invention, the polymerization time per onceis from 10 seconds to 30 minutes, preferably from 3 to 15 minutes.

The electrically conducting polymer layer formed on the dielectric filmby the method of the present invention is confirmed to have a lamellastructure or a fibril structure by an electron microphotograph.

The lamella structure and the fibril structure of the electricallyconducting polymer are considered to contribute to improvement of theone-dimensional property of the polymer chain, which is a factor ofelevating the electric conductivity, and also to the widespreadoverlapping among polymer chains, thereby giving preferred effects onthe elevation of electrical conductivity of the polymer solidelectrolyte and on the improvement of capacitor properties, such asrealization of low impedance.

In the method of the present invention, the number of dipping operationsmust be controlled so that the electrically conducting polymer compoundcan be formed to a thickness large enough to ensure the resistanceagainst moisture, heat, stress and the like. A desired solid electrolytelayer can be easily formed by repeating the above-described productionprocess 5 times or more, preferably from 8 to 30 times, per one anodesubstrate.

The step of forming a solid electrolyte for use in a solid electrolyticcapacitor is a step of alternately dipping the anode body obtained byforming a dielectric film on a valve acting metal, in themonomer-containing solution and in the oxidizing agent-containingsolution and drying it repeatedly to alternately attach the monomer andthe oxidizing agent to the anode body and allow the chemical oxidationpolymerization to proceed in air.

The temperature in the atmosphere varies depending on the kind andpolymerization method of the polymer composition and cannot beindiscriminately specified but in general, the temperature is preferablyin the range from −70° C. to 250° C.

The concentration of the monomer-containing solution is from 3 to 50mass %, preferably from 5 to 35 mass %, more preferably from 10 to 25mass %, and the concentration of the oxidizing agent-containing solutionis from 5 to 70 mass %, preferably from 15 to 50 mass %. The viscosityof each of the monomer-containing solution and the oxidizingagent-containing solution is 100 cP (centipoise) or less, preferably 30cP or less, more preferably from 0.6 to 10 cP.

According to the present invention, the solid electrolyte of anelectrically conducting polymer having a layer structure (lamellastructure or fibril structure) can be formed by the alternate dipping inthe monomer-containing solution and in the oxidizing agent-containingsolution. However, in order to further improve the one-dimensionalproperty of the polymer chain in this layer and generate moreoverlapping among the polymer chains, it has been found preferable notto perform the washing every each polymerization but perform the washingat the final stage. By doing so, the excess (unreacted) monomerremaining unreacted in one polymerization step can be polymerized in thesubsequent step, as a result, a solid electrolyte comprising anelectrically conducting polymer having a layer structure favored withwidespread overlapping among polymer chains can be formed.

In one preferred embodiment of the present invention, the process offorming a solid electrolyte includes a step of dipping the valve-actingmetal anode foil having formed thereon the above-described dielectricfilm layer in a solution containing an oxidizing agent (Solution 1) anda step of dipping it in a solution containing a monomer and a dopant(Solution 2). With respect to the order of dipping operations, an orderof dipping the valve-acting metal anode foil in Solution 1 and thendipping it in Solution 2 (regular order) may be used or a reversed orderof dipping the valve-acting metal anode foil in Solution 2 and thendipping it in Solution 1 may also be used.

In another embodiment, the process may include a step of dipping theanode foil in a solution containing an oxidizing agent and a dopant(Solution 3) and a step of dipping it in a solution containing a monomer(Solution 4). Also in this case, an order of dipping the anode foil inSolution 3 and then dipping it in Solution 4 (regular order) or areversed order of dipping the anode foil in Solution 4 and then dippingit in Solution 3 may be used. Solutions 1 to 4 each may be used in thesuspension state. Furthermore, the dipping may be replaced by coating.

The solvents in Solutions 1 to 4 may be the same, if desired, ordifferent solvent systems may be used. Depending on the kind of solvent,a drying step may be separately interposed between dipping steps ofSolution 1 and solution 2 or between dipping steps of Solution 3 andSolution 4. Furthermore, washing with a solvent may be performed afterthe formation of the solid electrolyte.

The valve-acting metal which can be used in the present invention is asimple metal such as aluminum, tantalum, niobium, titanium, zirconium,magnesium and silicon, or an alloy thereof. The metal may have any shapeas long as it is in the form of a porous shaped article such as anetched product of rolled foil or a sintered body of fine powder.

For the anode substrate, a porous sintered body of the above-describedmetal, a plate (including ribbon, foil and the like), a wire and thelike which are surface-treated by etching and the like, may be used,however, a plate and a foil are preferred. A known method may be usedfor forming an oxide dielectric film on the surface of this metal porousbody. For example, in the case of using a sintered body of tantalumpowder, the oxide film may be formed on the sintered body by theanodization in an aqueous phosphoric acid solution.

The thickness of the valve-acting metal foil varies depending on the useend, however, a foil having a thickness of about 40 to 300 μm is used.In order to produce a thin solid electrolytic capacitor, for example, inthe case of an aluminum foil, it is preferred to use an aluminum foilhaving a thickness of 80 to 250 μm and adjust the element having a solidelectrolyte thereon to have a maximum height (Rmax) of 250 μm or lessafter compression. The size and the shape of the metal foil also varydepending on the use end, however, the metal foil as a plate-likeelement unit preferably has a rectangular form having a width of about 1to about 50 mm and a length of about 1 to about 50 mm, more preferably awidth of about 2 to about 15 mm and a length of about 2 to about 25 mm.

Examples of the aqueous solution-type oxidizing agent which can be usedfor the formation of the solid electrolyte in the present inventioninclude peroxodisulfuric acid and Na, K and NH₄ salts thereof,cerium(IV) nitrate, ammonium cerium(IV) nitrate, iron(III) sulfate,iron(III) nitrate and iron(III) chloride. Examples of the organicsolvent-type oxidizing agent include ferric salts of an organic sulfonicacid, such as iron(III) dodecylbenzenesulfonate and iron(III)p-toluenesulfonate. Examples of the organic solvent used here includeγ-butyrdlactone and monohydric alcohols such as butanol and isopropanol.The concentration of the oxidizing agent solution is preferably from 5to 50 mass % and the temperature of the oxidizing agent solution ispreferably from −15 to 60° C.

The electrically conducting polymer constituting the solid electrolytefor use in the present invention is a polymer of an organic highmolecular monomer having a π electron-conjugate structure and thepolymerization degree thereof is from 2 to 2,000, more preferably from 3to 1,000, still more preferably from 5 to 200. Specific examples thereofinclude electrically conducting polymers containing, as a repeatingunit, a structure shown by a compound having a thiophene skeleton, acompound having a polycyclic sulfide skeleton, a compound having apyrrole skeleton, a compound having a furan skeleton or a compoundhaving an aniline skeleton, however, the electrically conducting polymeris not limited thereto.

Examples of the monomer compound having a thiophene skeleton includederivatives such as 3-methylthiophene, 3-ethylthiophene,3-propylthiophene, 3-butylthiophene, 3-pentylthiophene,3-hexylthiophene, 3-heptylthiophene, 3-octylthiophene, 3-nonylthiophene,3-decylthiophene, 3-fluorothiophene, 3-chlorothiophene,3-bromothiophene, 3-cyanothiophene, 3,4-dimethylthiophene,3,4-diethylthiophene, 3,4-butylenethiophene, 3,4-methylenedioxythiopheneand 3,4-ethylenedioxythiophene. These compounds are generally availableon the market or may be prepared by a known method (a method described,for example, in Synthetic Metals, Vol. 15, page 169 (1986)), however,the present invention is not limited thereto.

Specific examples of the monomer compound having a polycyclic sulfideskeleton include compounds having a 1,3-dihydro-polycyclic sulfide (alsocalled 1,3-dihydrobenzo-[c]thiophene) skeleton and compounds having a1,3-dihydronaphtho[2,3-c]thiophene skeleton. Furthermore, compoundshaving a 1,3-dihydroanthra[2,3-c]thiophene skeleton and compounds havinga 1,3-dihydronaphthaceno[2,3-c]thiophene skeleton may be used. Thesecompounds may be prepared by a known method, for example, by the methoddescribed in JP-A-8-3156.

In addition, compounds having a 1,3-dihydronaphtho[1,2-c]thiopheneskeleton such as 1,3-dihydrophenanthra[2,3-c]thiophene derivatives, andcompounds having a 1,3-dihydrotriphenylo[2,3-c]thiophene skeleton suchas 1,3-dihydrobenzo[a]anthraceno[7,8-c]thiophene derivatives, may alsobe used.

A compound arbitrarily containing nitrogen or N-oxide in the condensedring may also be used and examples thereof include1,3-dihydrothieno[3,4-b]quinoxaline,1,3-dihydrothieno[3,4-b]quinoxaline-4-oxide and1,3-dihydrothieno[3,4-b]quinoxaline-4,9-dioxide, however, the presentinvention is not limited thereto.

Examples of the monomer compound having a pyrrole skeleton includederivatives such as 3-methylpyrrole, 3-ethylpyrrole, 3-propylpyrrole,3-butylpyrrole, 3-pentylpyrrole, 3-hexylpyrrole, 3-heptylpyrrole,3-octylpyrole, 3-nonylpyrrole, 3-decylpyrrole, 3-fluoropyrrole,3-chloropyrrole, 3-bromopyrrole, 3-cyanopyrrole, 3,4-dimethylpyrrole,3,4-diethylpyrrole, 3,4-butylenepyrrole, 3,4-methylenedioxypyrrole and3,4-ethylenedioxypyrrole. These compounds are commercially available ormay be prepared by a known method, however the present invention is notlimited thereto.

Examples of the monomer compound having a furan skeleton includederivatives such as 3-methylfuran, 3-ethylfuran, 3-propylfuran,3-butylfuran, 3-pentylfuran, 3-hexylfuran, 3-heptylfuran, 3-octylfuran,3-nonylfuran, 3-decylfuran, 3-fluorofuran, 3-chlorofuran, 3-bromofuran,3-cyanofuran, 3,4-dimethylfuran, 3,4-diethylfuran, 3,4-butylenefuran,3,4-methylenedioxyfuran and 3,4-ethylenedioxyfuran. These compounds arecommercially available or may be prepared by a known method, however thepresent invention is not limited thereto.

Examples of the monomer compound having an aniline skeleton includederivatives such as 2-methylaniline, 2-ethylaniline, 2-propylaniline,2-butylaniline, 2-pentylaniline, 2-hexylaniline, 2-heptylaniline,2-octylaniline, 2-nonylanilin, 2-decylaniline, 2-fluoroaniline,2-chloroaniline, 2-bromoaniline, 2-cyanoaniline, 2,5-dimethylaniline,2,5-diethylaniline, 2,3-butyleneaniline, 2,3-methylenedioxyaniline and2,3-ethylenedioxyaniline. These compounds are commercially available ormay be prepared by a known method, however, the present invention is notlimited thereto.

Among these, the compounds having a thiophene skeleton or a polycyclicsulfide skeleton are preferred, and 3,4-ethylenedioxythiophene (EDT) and1,3-dihydroisothianaphthene are more preferred.

The solvent for the monomer of an organic polymer is preferably amonohydric alcohol (e.g., methyl alcohol, ethyl alcohol, n-propylalcohol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol,tert-butyl alcohol). The monomer concentration in the monomer solutionis not particularly limited and any concentration may be used.

The conditions for the polymerization of the compound selected from thegroup consisting of the above-described compounds are not particularlylimited and the polymerization may be easily performed after previouslyconfirming the preferred conditions by a simple experiment.

The solid electrolyte may be formed as a copolymer by using thecompounds selected from the group consisting of the above-describedcompounds in combination. In this case, the compositional ratio and thelike of polymerizable monomers depend on the polymerization conditionsand the preferred compositional ratio and polymerization conditions maybe confirmed by a simple experiment.

For example, a method where an EDT monomer and an oxidizing agent eachpreferably in the form of a solution are coated separately one afteranother or coated simultaneously on an oxide film layer of a metal foilto form a solid electrolyte (see, Japanese Patent No. 3,040,113 and U.S.Pat. No. 6,229,689), may be used.

3,4-Ethylenedioxythiophene (EDT) which is preferably used in the presentinvention is well soluble in the above-described monohydric alcohol butlow in the affinity for water, therefore, when EDT is contacted with anaqueous oxidizing agent solution of high concentration, thepolymerization of EDT aggressively proceeds on the interface thereof anda solid electrolyte layer of electrically conducting polymer with afibril structure or a lamella (thin layer-like) structure is formed.

Examples of the solvent for the solutions used in the production methodof the present invention and the solvent for washing after the formationof the solid electrolyte include ethers such as tetrahydrofuran (THF),dioxane and diethylether; ketones such as acetone and methyl ethylketone; aprotic polar solvents such as dimethylformamide, acetonitrile,benzonitrile, N-methylpyrrolidone (NMP) and dimethylsulfoxide (DMSO);esters such as ethyl acetate and butyl acetate; non-aromaticchlorine-based solvents such as chloroform and methylene chloride; nitrocompounds such as nitromethane, nitroethane and nitrobenzene; alcoholssuch as methanol, ethanol and propanol; organic acids such as formicacid, acetic acid and propionic acid; acid anhydrides of the organicacid (e.g., acetic anhydride); water; and mixed solvents thereof. Amongthese, preferred are water, alcohols, ketones and mixed systems thereof.

In forming the electrically conducting polymer for use in the presentinvention, an arylsulfonic acid-based dopant is used. Examples of thestarting material for dopant, which can be used, include salts ofbenzenesulfonic acid, toluenesulfonic acid, naphthalenesulfonic acid,anthracenesulfonic acid, anthraquinonesulfonic acid and the like.

The thus-produced solid electrolyte has an electric conductivity ofabout 0.1 to about 200 S/cm, preferably from about 1 to about 150 S/cm,more preferably from about 10 to about 100 S/cm.

In the present invention, the substrate having formed thereon anelectrically conducting polymer composition layer grown in thelongitudinal (thickness) direction by the oxidative polymerization isused after compressing it. By this compression, in the substrateschematically shown in FIG. 2, the difference [h₁−h₂] between themaximum thickness (h₁) and the minimum thickness (h₂) of the solidelectrolyte layer becomes small and at the same time, the substrateitself and electrically conducting polymer are also compressed to becomethinner, as a result, capacitor elements can be stably prepared with asmall variety of shape and capacitance.

Compression may be performed on a single capacitor element substratehaving formed thereon an electrically conducting polymer compositionlayer or on the outermost layer of a laminate body of a plurality ofcapacitor element substrates in the process of producing a multilayercapacitor.

The compression may be performed by superimposing and pressing thesubstrate having formed thereon an electrically conducting polymercomposition layer on a flat plate. The compression conditions may besufficient if these are within the range of not affecting the capacitorproperties. The substrate itself may be deformed by the compression.

More specifically, assuming that the maximum thickness and the minimumthickness of the electrically conducting polymer layer including thesubstrate before the compression are Hamax and Hamin, respectively, andthat the maximum thickness and the minimum thickness of the electricallyconducting polymer layer including the substrate after the compressionare Hbmax and Hbmin, respectively, the compression is performed suchthat the percentage decrease ΔH in the difference of thicknessrepresented by the following formula falls within a range of 5 to 95%.

${\Delta\;{H(\%)}} = {\left\lbrack {1 - \frac{\left( {{{Hb}\;\max} - {{Hb}\;\min}} \right)}{\left( {{{Ha}\;\max} - {{Ha}\;\min}} \right)}} \right\rbrack \times 100.}$

The compressibility of the entire substrate (including both a singleplate element and a multilayer plate element) having provided thereon asolid electrolyte layer is from 5 to 90%, preferably from 10 to 85%,more preferably from 15 to 80%.

The electric conductivity is about 0.1 to about 200 S/cm, preferablyfrom about 1 to about 150 S/cm, more preferably from about 10 to about100 S/cm.

The material of the flat plate for shaping used at the compression isnot particularly specified, however, a metal plate or material havingelasticity, for example, a plastic plate may be used. In this case, theflat plate itself may undergo elastic or plastic deformation at thecompression and the substrate may be embraced by the elastic body,however, this causes no problem as far as the substrate having formedthereon an electrically conducting polymer composition layer iscompressed to be thin. The substrate having formed thereon anelectrically conducting polymer composition layer may be compressedafter previously stacking a plurality of substrates or the compressionmay be repeated.

The pressure required for the compression is from 0.05 to 20 kg/mm²,preferably from 0.1 to 10 kg/mm², more preferably from 0.1 to 2 kg/mm².In the case where the minimum thickness of the element after compressionis limited, the distance between each flat plate for compression may becontrolled.

The retention time for the compression is from 0.01 seconds to 5minutes, preferably from 0.1 seconds to 30 seconds, more preferably from0.1 seconds to 10 seconds.

Immediately before the compression, the element may be heated to atemperature less than 200° C. or the flat plate may be heated to atemperature less than 230° C., or both of the element and the flat platemay also be heated.

In the compression step, a release agent may be used if appropriate forpreventing the element from adhering to the flat plate. For example,water, an organic solvent which does not adversely affect to cause thecathode layer comprising an electrically conducting polymer to dissolveor decompose and whose boiling point is lower than 100° C., or asurfactant which is removable in a later step may be used.

Also, the element may be prevented from adhering to the flat plate bysurface-treating the flat plate with plating, artificial diamondcoating, Teflon coating and the like.

When the dielectric film is flawed during the compression process, itcan be recovered by conducting the re-electrochemical formation or agingafter compression.

Through the above steps, a thin capacitor element having a uniformthickness can be prepared, and therefore element density in apredetermined-size capacitor case can be increased to break through theconventional upper limit of capacitance.

Furthermore, the capacitor element can be made thin and single-platecapacitor comprising such an element can be employed as a capacitor tobe placed in close contact with a circuit board.

According to the present invention, the solid electrolyte, covering theouter surface of the anode body and having a lamella or fibrilstructure, include continuous or independent spaces. Such spaces becomesmaller only in volume during the compression step, so that the densityof the solid electrolyte is increased while the lamella or fibrilstructure of solid electrolyte is maintained. Therefore, even if thethickness of the solid electrolyte becomes thin, its function to easeimpacts such as thermal stress or mechanical stress imposed during inthe steps for producing capacitor, such as molding step, does notchange. This useful structure can cope with various stresses imposed notonly in the production process but also from the environment where thecapacitor is actually used.

In the case where re-electrochemical formation is necessary, there-electrochemical formation conditions such as electrochemical formingvoltage may be the same as in the electrochemical formation, includingthe electrochemical forming solution. The electrochemical formingsolution is preferably a neutral salt such as ammonium adipate but maybe a phosphate. The re-electrochemical formation for recovery may beperformed as a step before fabricating a capacitor chip and may beperformed every time when the element is damaged or all damages may berecovered at a time.

Also, humidification aging for recovering the damaged element where avoltage is applied to the capacitor element or a capacitor chip in theatmosphere may be employed. Specifically, after an element or acapacitor chip is left standing under conditions of a temperature of 20to 95° C. and a humidity of 40 to 95% RH for 5 minutes to 100 hours, avoltage within 0.5 times of a rated voltage to a highest voltage nbtdestroying the capacitor may be applied under the atmosphere of roomtemperature to 230° C. Alternatively, a voltage from 0.5 times of therated voltage to a highest voltage not destroying the capacitor may beapplied in the atomosphere under the condition of 20 to 95° C. and 40 to95% RH.

When the damage by the compression is small, these recovery steps aresubstantially unnecessary.

On the thus-formed electrically conducting polymer composition layer, anelectrically conducting layer is preferably provided so as to attaingood electric contact with the cathode lead terminal. For example, anelectrically conducting paste is solidified, a metal is plated ordeposited, or an electrically conducting resin film is formed to workout to electrically conducting layer.

In the present invention, the compression may be performed after theelectrically conducting layer is formed. This is particularly effective.For example, in the case of an electrically conducting layer containingan elastic body, plastic deformation occurs by the compression, tofurther reduce the thickness and an effect of smoothing the electricallyconducting layer surface is also provided.

The thus-obtained solid electrolytic capacitor element is usuallyconnected with a lead terminal and then a jacket is applied to theelement by using resin molding, a resin case, a metal-made jacket case,resin dipping or the like, thereby completing a capacitor product forvarious uses.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view of a solid electrolytic capacitor usinga capacitor element.

FIG. 2 is a schematic longitudinal cross-sectional view of the capacitorelement part of Example 1.

FIG. 3 is a cross-sectional view of a solid electrolytic capacitorobtained by stacking capacitor elements.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention is described in detail below by referring torepresentative Examples, however, these are given for merelyillustrating the invention and the present invention is not limitedthereto.

EXAMPLE 1

A formed aluminum foil (thickness: 100 μm) was cut into a size of 3 mm(short axis direction)×10 mm (long axis direction) and a polyimidesolution was circumferentially coated on both surfaces to a width of 1mm to section the surface area into a 4-mm portion and a 5-mm portion inthe long axis direction, and then dried to form a masking. The 3 mm×4 mmportion of this formed foil was electrochemically formed with an aqueous10 mass % ammonium adipate solution by applying a voltage of 4 V to forman oxide dielectric film on the cut end part. Thereafter, this 3 mm×4 mmportion of the aluminum foil was dipped in 1.2 mol/L of an isopropylalcohol (IPA) solution having dissolved therein3,4-ethylenedioxythiophene for 5 seconds, dried at room temperature for5 minutes, and then dipped for 5 seconds in 2 mol/L of an aqueousammonium persulfate solution containing sodium 2-anthraquinonesulfonateadjusted to a concentration of 0.07 mass %. Subsequently, this aluminumfoil was left standing in an air at 40° C. for 10 minutes, therebyperforming the oxidative polymerization. By repeating the dipping stepand the polymerization step 25 times in total, a solid electrolyte layerof an electrically conducting polymer was formed on the outer surface ofthe aluminum foil. The finally produced poly(3,4-ethylenedioxythiophene)was washed with warm water at 50° C. and then dried at 100° C. for 30minutes to complete the formation of the solid electrolyte layer.

Using a thickness gauge (manufactured by Peacock Corp.: DigitalIndicator DG-205 (accuracy of 3 μm)), the thickness was measured byslowly putting the aluminum foil into the measuring part of thethickness gauge. As a result, the largest thickness (h₁) shown in theschematic view of FIG. 2 was 260 μm, the smallest thickness (h₂) was 210μm, and the difference (h₁−h₂) in the film thickness was 50 μm.

After this measurement of thickness, the aluminum foil in the portionwhere the electrically conducting polymer composition layer was formedwas compression-molded at the pressure of 1.5 kg/mm² in a metal moldwith a minimum clearance of 140 μm. Then, the thickness was measured inthe same manner. As a result, the maximum thickness (h₁) shown in theschematic view of FIG. 2 was 180 μm, the minimum thickness (h₂) was 170μm, and the difference (h₁−h₂) in the film thickness was 10 μm. Thepercentage decrease (ΔH) in the difference of thickness of the solidelectrolyte layer after compression was 80% and the compressibilityratio was approximately 30%.

After that, the 3 mm×4 mm portion having a solid electrolyte layerformed thereon and provided with an anode-connecting point in theportion having no solid electrolyte formed thereon was dipped in a 15mass % ammonium adipate, and then applied a voltage of 3.8V to perform are-electrochemical formation.

Then, as shown in FIG. 3, carbon paste and silver paste were applied tothe aluminum foil in the portion where the electrically conductingpolymer composition layer was formed. Four sheets of the thus-preparedaluminum foils were stacked and a cathode lead terminal was connectedthereto. To the portion where the electrically conducting polymer wasnot formed, an anode lead terminal was connected by welding. Theresulting element was molded with an epoxy resin and aged at 125° C. for2 hours by applying thereto a rated voltage (2V) In this way, 30 unitsin total of capacitors were fabricated.

These 30 units of capacitor elements were measured on the initialproperties, that is, capacitance and loss factor (tan δ×100%) at 120 Hz,equivalent series resistance (ESR) and leakage current. The leakagecurrent was measured one minute after the rated voltage was applied. InTable 1, respective averages of these measured values, the rate ofdefective units having a leakage current of 0.002 CV or more are shown.The average of the leakage current values is a value calculatedexclusive of such defective units.

EXAMPLES 2(1) TO 2(3)

A solid electrolyte was formed under the same production conditions asin Example 1 and subjected to various combinations of compression andstacking.

EXAMPLE 2(1)

A capacitor element was fabricated in the same manner as in Example 1except that each of the formed aluminum foil substrate having thereon asolid electrolyte was compressed in the thickness direction after carbonpaste and silver paste were attached on the surface, four of thusobtained aluminum foils were stacked and a cathode lead terminal wasconnected thereto.

EXAMPLE 2(2)

A capacitor element was fabricated in the same manner as in Example 1except that the substrate having provided thereon a solid electrolytewas compressed in the thickness direction, four of thus obtainedcapacitor elements were stacked, the stacked body was compressed in thethickness direction, carbon paste and silver paste were attached thereonand a cathode lead terminal was connected thereto.

EXAMPLE 2(3)

A capacitor element was fabricated in the same manner as in Example 1except that four substrates each having provided thereon a solidelectrolyte were stacked, the stacked body was compressed in thethickness direction, carbon paste and silver paste were attached thereonand a cathode lead terminal was connected thereto.

The obtained capacitors were evaluated on the properties in the samemanner as in Example 1 and the results are shown in Table 1.

EXAMPLE 3

30 Units of capacitors were fabricated in the same manner as in Example1 except that pyrrole was used in place of 3,4-ethylenedioxythiophene,the pyrrole solution was dried at 3° C. for 5 minutes after theimpregnation, and polymerization was performed at 5° C. for 10 minutesafter impregnation in an oxidizing agent solution.

The maximum thickness (h₁) of the solid electrolyte layer was measuredin the same manner as in Example 1 and found to be 290 μm, the minimumthickness (h₂) was 230 μm, and the difference (h₁−h₂) in the filmthickness was 60 μm. After the subsequent compression, the maximumthickness (h₁) was 200 μm, the minimum thickness (h₂) was 180 μm, andthe difference (h₁−h₂) in the film thickness was 20 μm. The percentagedecrease (ΔH) in the difference of thickness of the solid electrolytelayer after compression was 66.7%.

The obtained capacitor elements were evaluated on the properties in thesame manner as in Example 1 and the results are shown in Table 1.

COMPARATIVE EXAMPLE 1

30 Units of capacitors were fabricated in the same manner as in Example1 except that the capacitor element produced was used withoutcompression-molding.

The maximum thickness (h₁) of the solid electrolyte layer was measuredin the same manner as in Example 1 and found to be 260 μm, the minimumthickness (h₂) was 210 μm, and the difference (h₁−h₂) in the filmthickness was 50 μm.

The obtained capacitor elements were evaluated on the properties in thesame manner as in Example 1 and the results are shown in Table 1.

COMPARATIVE EXAMPLE 2

30 Units of capacitor elements were fabricated in the same manner as inExample 1 except that the capacitor element produced by performingpolymerization 15 times was used without compression.

The maximum thickness (h₁) of the solid electrolyte layer was measuredin the same manner as in Example 1 and found to be 180 μm, the minimumthickness (h₂) was 120 μm, and the difference (h₁−h₂) in the filmthickness was 60 μm.

The obtained capacitor elements were evaluated on the properties in thesame manner as in Example 1 and the results are shown in Table 1.

TABLE 1 Initial Properties Loss Leakage Capacitance Factor ESR CurrentDefective Example μF % Ω μA Rate 1 109 0.7 0.007 0.03 0/30 2 (1) 108 0.90.008 0.06 0/30 2 (2) 109 1.6 0.017 0.03 0/30 2 (3) 110 1.8 0.018 0.040/30 3 105 1.7 0.014 0.09 1/30 Comparative  108* 3.6 0.025 0.05 1/30Example 1 Comparative 107 1.9 0.020 0.15 7/30 Example 2 *Not molded(Element(s) partially protruding out disturbed the molding.)

It is seen from the results of Examples 1 to 3 and Comparative Example 1and 2 that the solid electrolytic capacitor is excellent in that, byextremely reducing the thickness difference (ΔH) through compression ofthe solid electrolyte layer, the capacitor can obtain properties such asa high capacitance and a low ESR and is reduced in the leakage currentand defective ratio.

EXAMPLE 4

Two sheets of substrates each obtained by forming an electricallyconducting composition layer on an aluminum foil were stacked, theportion where the electrically conducting polymer composition layer wasformed was compression-molded, and the thickness was measured in thesame manner as in Example 1. As a result, the maximum thickness (h₁) ofthe solid electrolyte layer in the element where 2 substrates werestacked was 430 μm, the minimum thickness (h₂) was 400 μm, and thedifference (h₁−h₂) in the film thickness was 30 μm.

EXAMPLE 5

After two sheets of substrates each obtained by forming an electricallyconducting polymer composition layer on an aluminum foil were stacked,another two sheets of substrates whose portion having an electricallyconducting polymer composition layer had been compression-molded weresuperposed thereon and further compression-molded to prepare an elementwhere 4 substrates were stacked. The thickness of the solid electrolytelayer in this element was measured in the same manner as in Example 1,as a result, the maximum thickness (h₁) of the solid electrolyte layerwas 780 μm, the thickness minimum (h₂) was 760 μm, and the difference(h₁−h₂) in the film thickness was 20 μm.

INDUSTRIAL APPLICABILITY

The solid electrolytic multilayer capacitor of the present invention,which uses a thin capacitor element stably prepared with a small varietyin shape through a process where a solid electrolyte comprising anelectrically conducting polymer of an organic polymer is provided on thedielectric film surface of a porous valve-acting metal substrate and thesubstrate is compressed in the thickness direction, has ahigh-capacitance, small-size with low height, and a stable performancewithout short-circuit failure.

1. A solid electrolytic capacitor comprising a capacitor elementobtainable by compressing a porous valve-acting metal substrate havingon the dielectric film surface thereof a solid electrolyte layercontaining an electrically conducting polymer in the thickness directionand re-electrochemical formation after the compressing step.
 2. Thesolid electrolytic capacitor as claimed in claim 1, wherein in thecapacitor element, the porous valve-acting metal substrate having on thedielectric film surface thereof a solid electrolyte layer containing anelectrically conducting polymer is compressed in the thickness directionand a cathode layer is provided on the solid electrolyte layer.
 3. Thesolid electrolytic capacitor as claimed in claim 2, comprising acapacitor element obtained by compressing a porous valve-acting metalsubstrate having on the dielectric film surface thereof a solidelectrolyte layer containing an electrically conducting polymer in thethickness direction to homogenize the thickness of the electricallyconducting polymer layer and then providing a cathode layer on the solidelectrolyte layer.
 4. The solid electrolytic capacitor as claimed inclaim 1, wherein the solid electrolyte containing an electricallyconducting polymer to be provided on the dielectric film on the porousvalve-acting metal is formed by chemical polymerization orelectrochemical polymerization.
 5. The solid electrolytic capacitor asclaimed in claim 1, wherein the thickness of the element having thereona solid electrolyte layer has a maximum height (Rmax) of 250 μm or lessafter the compression.
 6. The solid electrolytic capacitor as claimed inclaim 1, wherein, assuming that the maximum thickness and the minimumthickness of the electrically conducting polymer layer including thesubstrate before the compression are Hamax and Hamin, respectively, andthat the maximum thickness and the minimum thickness of the electricallyconducting polymer layer including the substrate after the compressionare Hbmax and Hbmin, respectively, the percentage decrease AH in thedifference of thickness represented by the following formula is within arange of 5 to 95%:${\Delta\;{H(\%)}} = {\left\lbrack {1 - \frac{\left( {{{Hb}\;\max} - {{Hb}\;\min}} \right)}{\left( {{{Ha}\;\max} - {{Ha}\;\min}} \right)}} \right\rbrack \times 100.}$7. The solid electrolytic capacitor as claimed in claim 1, wherein thecompressibility of the entire substrate having thereon a solidelectrolyte layer is from 5 to 90%.
 8. The solid electrolytic capacitoras claimed in claim 1, wherein the electrically conducting polymer asthe solid electrolyte is formed on the valve-acting metal substratehaving a dielectric film by solution chemical oxidative polymerizationor vapor-phase chemical oxidative polymerization using a monomer of anorganic polymer.
 9. The solid electrolytic capacitor as claimed in claim1, wherein the electrically conducting polymer as the solid electrolyteis formed by repeating an operation of alternately dipping thevalve-acting metal substrate having a dielectric film in a solutioncontaining a monomer of an organic polymer and in a solution containingan oxidizing agent.
 10. The solid electrolytic capacitor as claimed inclaim 1, wherein the porous valve-acting metal substrate has a plate- orfoil-like shape.
 11. The solid electrolytic capacitor as claimed inclaim 1, wherein the porous valve-acting metal is a simple metalselected from a group consisting of aluminum, tantalum, niobium,titanium, zirconium, magnesium and silicon, or an alloy thereof.
 12. Thesolid electrolytic capacitor as claimed in claim 1, wherein the monomerof the organic polymer for forming the electrically conducting polymeris a compound containing a 5-member heterocyclic ring, or a compoundhaving an aniline skeleton.
 13. The solid electrolytic capacitor asclaimed in claim 12, wherein the compound containing a 5-memberheterocyclic ring is a compound having a thiophene skeleton or apolycyclic sulfide skeleton.
 14. The solid electrolytic capacitor asclaimed in claim 13, wherein the monomer compound having a thiopheneskeleton is 3-ethylthiophene, 3-hexylthiophene, 3,4-dimethylthiophene,3,4-methylenedioxythiophene or 3,4-ethylenedioxythiophene.
 15. The solidelectrolytic capacitor as claimed in claim 1, wherein a part of thesolid electrolyte layer formed of the electrically conducting polymerhas a lamella structure or a fibril structure.
 16. A solid electrolyticmultilayer capacitor obtained by stacking a plurality of capacitorelements described in claim
 1. 17. A solid electrolytic multilayercapacitor comprising a capacitor element obtained by stacking aplurality of porous valve-acting metal substrates each having on thedielectric film surface thereof a solid electrolyte layer comprising anelectrically conducting polymer resulting from oxidative polymerizationof a monomer of an organic polymer with an oxidizing agent, compressingthe multilayer substrate in the thickness direction, providing a cathodelayer on the outer surface of the solid electrolyte layer, andre-electrochemical formation after the compressing step.
 18. The solidelectrolytic multilayer capacitor as claimed in claim 17, wherein thecompressibility of the entire multilayer substrate having providedthereon solid electrolyte layers is from 5 to 90%.
 19. A method forproducing a solid electrolytic capacitor, comprising forming a solidelectrolyte layer of an electrically conducting polymer on the surfaceof a porous valve-acting metal substrate having a dielectric film byusing a solution containing a monomer for forming an electricallyconducting polymer under the action of an oxidizing agent and a solutioncontaining an oxidizing agent, compressing the substrate having providedthereon an electrically conducting polymer in the thickness directionand providing a cathode layer on the solid electrolyte layer, furthercomprising a re-electrochemical formation step after the step ofcompressing the substrate having provided thereon a solid electrolytelayer in the thickness direction.
 20. The method for producing a solidelectrolytic capacitor as claimed in claim 19, wherein the entiresubstrate having provided thereon a solid electrolyte layer iscompressed at a compressibility of 5 to 90%.
 21. The method forproducing a solid electrolytic capacitor as claimed in claim 19, whereinassuming that the maximum thickness and the minimum thickness of theelectrically conducting polymer layer including the substrate before thecompression are Hamax and Hamin, respectively, and that the maximumthickness and the minimum thickness of the electrically conductingpolymer layer including the substrate after the compression are Hbmaxand Hbmin, respectively, the compression is performed such that thepercentage decrease ΔH in the difference of thickness represented by thefollowing formula is within a range of 5 to 95%:${\Delta\;{H(\%)}} = {\left\lbrack {1 - \frac{\left( {{{Hb}\;\max} - {{Hb}\;\min}} \right)}{\left( {{{Ha}\;\max} - {{Ha}\;\min}} \right)}} \right\rbrack \times 100.}$22. The method for producing a solid electrolytic capacitor as claimedin chain 19, which comprises a humidification aging step after the stepof compressing the substrate having provided thereon a solid electrolytelayer in the thickness direction.
 23. The method for producing a solidelectrolytic capacitor as claimed in claim 22, wherein thehumidification aging step is performed at an electrochemical formingvoltage lower than the sparking voltage under the conditions of 20 to95° C. and 40 to 95% RH.
 24. A method for producing a solid electrolyticcapacitor, comprising forming a solid electrolyte layer of anelectrically conducting polymer on the surface of a porous valve-actingmetal substrate having a dielectric film by using a solution containinga monomer for forming an electrically conducting polymer under theaction of an oxidizing agent and a solution containing an oxidizingagent, stacking a plurality of substrates each having provided thereonan electrically conducting polymer, compressing the multilayer substratein the thickness direction and providing a cathode layer on the outersurface of the solid electrolyte layer, further comprising are-electrochemical formation step after the step of compressing thesubstrate having provided thereon a solid electrolyte layer in thethickness direction.
 25. A method for producing a solid electrolyticcapacitor, comprising forming a solid electrolyte layer of anelectrically conducting polymer on the surface of a porous valve-actingmetal substrate having a dielectric film by using a solution containinga monomer for forming an electrically conducting polymer under theaction of an oxidizing agent and a solution containing an oxidizingagent, compressing the substrate having provided thereon an electricallyconducting polymer in the thickness direction, providing a cathode layeron the solid electrolyte layer, and compressing the cathode layer in thethickness direction, further comprising a re-electrochemical formationstep after the step of compressing the substrate having provided thereona solid electrolyte layer in the thickness direction.